The Minimum Yellow Timing for Ramp Meters

The minimum Yellow timing is an important timing factor that affects metering rate for multiple-vehicle-per-green, such as two-vehicle-per-green, type of operations. In review of the current ramp meter timing practices, it was found that the minimum Yellow timing does not consider the dilemma zone issue for the approaching motorists, and therefore may lead to red-light running. An analytic framework was developed to determine the minimum Yellow timing by integrating the ramp meter timing logic and dilemma zone removal practices. Factors such as roadway geometry, driver and vehicle characteristics, and detector layout are considered. For two-vehicle-per-green type of operations, an evaluation indicated that the minimum Yellow should be timed around 3.6 seconds to consider the situation when the 2nd vehicle is approaching. Such a long but necessary minimum Yellow timing will increase the minimum cycle length to about 7.7 seconds and hence reduce the release capacity by about 10%.